1. Field of the Invention
This invention relates to apparatus for generating seismic signals useful for geophysical mapping and exploration. Seismic signals are generated by means of a projectile fired from a gun. The gun is mounted on a base which is, in the usual form, a cylindrical member with sidewalls and a top plate. Means are provided for moving the base about on the surface of the earth with the base supported on its lower end when a projectile is fired. The invention is directed towards improvements in the mounting of a spatter plate and diaphragm to more effectively intercept gas, liquids, and solid objects which are ejected when a projectile is fired to generate a seismic signal.
2. Description of the Prior Art
A brief discussion of the prior art is set out in the parent application of which this is a continuation-in-part. The concept to which this invention is relevant is that of providing a portable seismic energy source which generates a seismic signal by means of a gun mounted to fire a projectile into the earth. While the gun may be supported in a variety of ways, a method found to be successful is the provision of a base on which the gun is supported with a wheeled arrangement so that it can be moved about on the surface of the earth. When a seismic signal is to be generated the base is supported directly on the surface of the earth. When a projectile is fired the gas of the explosion must be vented. In addition, liquids and solid objects are ejected by the force of impact of the projectile and by the force of the firing gases. In order to prevent injury to operators or bystanders, it is important that the gas, liquid, and solid objects be intercepted.
It has been discovered that the safety of the operation of a portable seismic source is improved by the use of a flexible diaphragm in conjunction with the base and, this is the subject matter of Application Ser. No. 188,370 above referenced. It has been further discovered that improved diaphragm performance and extended life of the diaphragm can be obtained by an arrangement wherein a spatter plate of metal is positioned within the base and spaced above the ground to receive the impact of a majority of the liquids, gases and solids which are ejected as a projectile impacts the earth. The diaphragm can be further employed to intercept other objects which do not strike the spatter plate while at the same time permitting the upward passage of gases to equalize pressure within the base by mounting the diaphragm around the periphery of the base and over the top of the spatter plate. It is this arrangement to which the present invention is directed.